From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2001:470:1f0b:db:abcd:42:0:1]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id E2B2B1A0CBC for ; Tue, 20 Jan 2015 22:21:47 +1100 (AEDT) Date: Tue, 20 Jan 2015 12:21:24 +0100 (CET) From: Thomas Gleixner To: Preeti U Murthy Subject: Re: [PATCH] idle/tick-broadcast: Exit cpu idle poll loop when cleared from tick_broadcast_force_mask In-Reply-To: <20150119052754.20256.54721.stgit@preeti.in.ibm.com> Message-ID: References: <20150119052754.20256.54721.stgit@preeti.in.ibm.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: peterz@infradead.org, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 19 Jan 2015, Preeti U Murthy wrote: > An idle cpu enters cpu_idle_poll() if it is set in the tick_broadcast_force_mask. > This is so that it does not incur the overhead of entering idle states when it is expected > to be woken up anytime then through a broadcast IPI. The condition that forces an exit out > of the idle polling is the check on setting of the TIF_NEED_RESCHED flag for the idle thread. > > When the broadcast IPI does arrive, it is not guarenteed that the handler sets the > TIF_NEED_RESCHED flag. Hence although the cpu is cleared in the tick_broadcast_force_mask, > it continues to loop in cpu_idle_poll unnecessarily wasting power. Hence exit the idle > poll loop if the tick_broadcast_force_mask gets cleared and enter idle states. > > Of course if the cpu has entered cpu_idle_poll() on being asked to poll explicitly, > it continues to poll till it is asked to reschedule. > > Signed-off-by: Preeti U Murthy > --- > > kernel/sched/idle.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > index c47fce7..aaf1c1d 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -47,7 +47,8 @@ static inline int cpu_idle_poll(void) > rcu_idle_enter(); > trace_cpu_idle_rcuidle(0, smp_processor_id()); > local_irq_enable(); > - while (!tif_need_resched()) > + while (!tif_need_resched() && > + (cpu_idle_force_poll || tick_check_broadcast_expired())) You explain the tick_check_broadcast_expired() bit, but what about the cpu_idle_force_poll part? Thanks, tglx